1. Field of the Invention
The invention relates to a vehicle with central wheel drive, in particular a wheelchair or stand-up wheelchair, with a chassis and a seat device arranged on the chassis, the chassis having a front part and a rear part which are connected to each other in an articulated manner by means of a joint, and also two central wheels which can be motor-driven separately from each other, two front wheels and at least one rear wheel.
2. State of the Art
U.S. Pat. No. 5,904,214 discloses a wheelchair with central wheel drive with two central wheels, two front wheels in the form of pivot wheels and a rear wheel. The seat is arranged over the central wheels. Each of the two central wheels can be driven separately by a motor. This has the advantage that the wheelchair can be turned in a narrow space, for example in an elevator car. In order in this way to turn on site, the user of the wheelchair actuates the controller in such a way that the two central wheels are rotated in mutually opposite directions. This turns the user, along with the wheelchair, about his or her own axis. The front wheels may not obstruct turning. This is why the front wheels are in the form of pivot wheels. This wheelchair has the drawback that the front wheels have to be in the form of pivot wheels in order not to obstruct turning. There is therefore little space for the footrest. A particular drawback of this wheelchair is the fact that it is not possible, when travelling slowly, to surmount obstacles exceeding a certain height.
A six-wheeled wheelchair, in which a two-armed lever is articulated by means of a joint on each side of the chassis, has become known from WO 2005/051279. A wheel is arranged on each lever arm. The wheels of this pair of wheels are coupled to each other by a chain or a toothed gearing and can be jointly driven by a motor. The arrangement of the two pairs of wheels and the rear wheels is selected in such a way that the weight of the user of the chair is distributed roughly uniformly onto the pairs of wheels and the rear wheels. From the point of view of their function, the aforementioned pairs of wheels are thus front wheels. The articulated arrangement of the two-armed lever on the chassis ensures that both wheels of the pairs of wheels remain in contact with the ground at all times, even when travelling on uneven terrain. This wheelchair does not have the advantages of the wheelchair with central drive as described hereinbefore. It is not possible to turn on site.
Vehicles with central drive, in particular wheelchairs, should also be able to surmount obstacles. When the front wheel of a vehicle strikes an obstacle, for example the edge of a kerb, two force components become active: a first force components extending parallel and counter to the direction of travel and a second force component which is directed upward, perpendicularly to the direction of travel. The higher the edge to be surmounted of the obstacle, the greater the first force component becomes. The necessary drive force must thus be all the greater in order to be able to surmount the obstacle. If the motor power is relatively low, the obstacle cannot be surmounted when travelling slowly. In order to be able to surmount the obstacle even when travelling slowly, the diameter of the front wheel can be increased in size. However, this is usually undesirable, either because there is little available space or on account of the undesirable increase in weight associated therewith.
U.S. Pat. No. 5,964,473 proposes providing before the front wheel a further wheel, known as a lift wheel. The lift wheel is arranged in a somewhat raised manner and is thus not normally in contact with the ground. When surmounting an obstacle, the lift wheel firstly strikes the obstacle and lifts the front of the chassis somewhat upward and in this way makes it easier for the front wheel to surmount the obstacle. However, the fact that the use of lift wheels makes the wheelchair more expensive is disadvantageous.
The surmounting of obstacles and the travelling behaviour of the vehicle, for example on snow-covered carriageways, can be improved if not only the central wheels, but also the front and/or rear wheels are motor-drivable. Thus, for example, U.S. Pat. No. 5,904,214 provides motor-drivable rear wheels. WO 2006/136046 discloses a wheelchair in which a central wheel, a front and/or rear wheel is arranged on each side, an endless chain serving as the common drive for these wheels. The wheelchair described therein requires special pivot wheels having at least one spring joint. This increases the manufacturing costs of the wheelchair.
The wheelchairs described hereinbefore according to U.S. Pat. No. 5,904,214, U.S. Pat. No. 5,964,473 and WO 2006/136046 all have the advantage mentioned at the outset of being able to turn in a narrow space. However, these wheelchairs are not stand-up wheelchairs and therefore permit only a person sitting down, but not a person standing up, to carry out a rotation about his own axis.
DE 198 16 879 describes a stair-climbing wheelchair with a combined wheel and crawler drive having four rotatable and pivotable pivot arms. In contrast to wheelchairs with central wheel drive, the described wheelchair is of much more complex design and does not allow turning in a very narrow space.
The wheelchair according to US 2007/0152427 is not a wheelchair with central wheel drive either. This wheelchair has in principle four or eight articulated wheel units, the wheels of which can be individually motor-driven.
WO 2005/051279 describes an electric wheelchair having a frame, arranged on the front of which are two drive shafts which can be driven by electric motors. Each drive shaft drives two successively arranged front wheels via a gear mechanism. Two rear wheels are also provided. The description expressly refers to pairs of front wheels arranged in-line. There is thus no wheelchair with central wheel drive. It is thus also not possible to turn the wheelchair described in a narrow space by way of rotation of central wheels in mutually opposite directions.
GB 2 325 903 discloses a vehicle with a chassis having a front part and a rear part which are connected to each other in an articulated manner by means of a joint. The front wheels and the central wheels, which can be driven by a four wheel drive with one or more motors, are arranged on the front part. On flat ground, both the front and the rear wheels are in contact with the ground; this has the drawback that it is not possible to turn in a narrow space, because the non-steerable front wheels prevent this. It is also almost impossible to surmount an obstacle when travelling forward without a run-up. Instead, reversing is expressly prescribed in order to surmount the obstacle (page 7, lines 2 ff.). In order to allow an obstacle to be surmounted, the rear wheels are arranged in a raised manner. They are not normally in contact with the ground. A sensor is also provided that can be used to control an actuator which pivots the front part in relation to the rear part in order to raise a pair of auxiliary wheels by means of a lifting system so that the pair of auxiliary wheels can easily surmount the obstacle. For the same purpose, the pivoting of the rear part also causes raising of the central wheels. This design is complex and expensive and has, apart from the aforementioned drawback of turning in a narrow space being impossible, the further drawback that a relatively large obstacle can be surmounted only when reversing.
It is an advantage of the present invention to provide a vehicle with central wheel drive, in particular a wheelchair or stand-up wheelchair, which is able to surmount relatively large obstacles even at relatively low speed, has good travelling properties even, for example, on a snow-covered carriageway, but still has the advantages of central wheel drive, including in particular the capacity to turn in a narrow space. A stand-up wheelchair should enable the user to perform a rotation about his or her own axis both in the sitting position and in the standing position.